1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor used in a copier, a printer, etc., and a process cartridge and an electrophotographic apparatus using the same.
2. Description of the Related Art
As photoconductive materials in an electrophotographic photoreceptor, a variety of inorganic and organic materials have been known. Organic photoreceptors employing photoconductive organic materials have come to be mainly used in the art for their advantages of satisfactory film forming properties, flexibility, low cost and the like.
As electrophotographic photoreceptors comprising an organic photosensitive layer on an electroconductive substrate can be mentioned: multilayer photoreceptors in which the photosensitive layer is function-separated into a charge-generating layer and a charge-transporting layer; and single-layer photoreceptors in which charge-generating and charge-transporting functions are included in a single layer. Among these multilayer electrophotographic photoreceptors are generally used in view of easier control of the characteristics of the photoreceptor by the function-separation.
Further, in the multilayer photoreceptors, interposing an interlayer consisting of various materials between the electroconductive substrate and the photosensitive layer of the photoreceptor has been tried, in order to reduce drawbacks due to the repetitive use of the charging-exposure processes, such as reduction of charging, increase in dark decay, increase in residual potential and image quality defects.
This interlayer is provided for the purpose of preventing unnecessary charge injection from the electroconductive substrate; maintaining adequate reception of the charges generated in the charge-generating layer at exposure; and improving adhesiveness between the photosensitive layer and the electroconductive substrate.
Meanwhile, when charge-generating materials are used for a photosensitive material for a semiconductor laser, it is necessary to firstly extend the photosensitive wavelengths into the long-wavelength region, and then improve the electrical properties and durability of the formed photoreceptor. Further, phthalocyanine compounds, etc., exhibiting sensitivity in the wavelength ranges of semiconductor lasers, have attracted attention.
However, depending on the composition of the charge-generating layer, sometimes a charge carrier which should input to the substrate side, is re-combined with charge carrier of the opposite polarity in the charge-generating layer, or accumulates at the boundary of the interlayer and the charge-generating layer to form a space charge barrier, thereby reducing the charging potential with repetitive use and increasing the residual potential. As a means for preventing such drawbacks, it has been suggested that an electron-donating material be contained in the interlayer. For example, the following have been tried; providing a barrier layer comprising a non-hydrophilic peptide polymer and an electron-donating material or an electron-accepting material (for example, refer to JP-B No. 61-35551); providing an interlayer comprising an electron-donating material (for example, refer to JP-A No. 60-218655); providing an interlayer comprising a hydrazone compound (for example, refer to JP-A No. 61-80158); or providing an interlayer comprising a charge-transporting material such as imidazole, pyrazoline, thiazole, oxadiazole, oxazole, hydrazone, ketazine, azine, carbazole, polyvinylcarbazole, etc. (for example, refer to JP-A No. 61-204640).
However, accompanying the increases in speed and durability of copiers in recent years, there have been further demands for an electrophotographic photoreceptor with higher sensitivity in photo-responsiveness and higher durability.
The invention is to provide an excellent electrophotographic photoreceptor which allows charges to be easily moved between an interlayer and a charge-transporting layer, and has high sensitivity and low residual potential. Further, the invention provides an electrophotographic apparatus and a process cartridge, wherein even with prolonged repetitive use, low residual potential is not deteriorated while maintaining high sensitivity, thereby obtaining suitable images having no decrease in image concentration and no smudging.